# DSP control PLL chip

Hi:

I meet a problem about PLL chip's controlling .

I use TMS320F28335 (DSP)  to control the HMC833 (PLL) . I have checked the hardware  and  software over and over again.  Both of them are  correct . Furthermore, I confirm the clock of SPI  is lower than 10MHz through delay function . But the signal is still not  appeared.

The same PLL , I use MCU  to   control  it . It output correctly. And I use ARM to control it , the  output is also correct.

MCU,ARM and DSP is different in system clock . The system clock of MCU and ARM  is lower than 30MHz.  The system clock of  DSP is 125 MHz. But I have decreased the clock of SPI  through delay function.

It's worth paying attention to the SPI line, it's guide line soldering and not PCB wiring. Concerning this , I have decrease the SPI clock cycle in 2.5 ms.

I really don't know where I didn't notice . Can you  give me some suggestions.

• After power-on the HMC833 will wait for a rising edge on SEN or SCLK:

If there is any noise or uncontrolled transitions on the SPI lines from your controller after power-on the HMC833 may enter the wrong mode.  Check if you can toggle LD/SDO (pin 33)  by writing the following sequence:

Reg 0x0F=0xC0 sets LD/SDO low

Reg 0x0F=0xE0 sets LD/SDO high

Reg 0x0F=0xC0 sets LD/SDO low

If the pin does not toggle the HMC833 may be operating in the wrong SPI mode.

• Thanks for your reply . It works effectivly.Thanks again.

•             Hi,:

I have a issue . I want  to design a TDD transceiver . I  choose  the HMC392ALC4  as LNA.  The chip  of HMC392ALC4  need to be  controlled in the mode of TDD.   It need to be powered on and off.But  I didn't find the  response time  in the datasheet. Can you help me  confirm  the  response  time of  Powering on and  off . Thanks very much .

Look forward to  your  good message.

• Hi XJLee,

The switching time of HMC392ALC4 alone will typically be below 1uS. Would that meet your requirement, if not for switching times below that we need to check?

ps. If you can open a new EZ post for question about another part, you will be able to get a faster response.

Best,

Kagan

•  Hi,Kagan: